With increasing requirements on riding comfort and off-road performance of vehicles, the independent suspension technology is gradually used in multi-axle wheel type heavy duty vehicles which have higher requirements on the off-road performance. FIG. 1 is an existing independent suspension device for a multi-axle steering wheel type heavy duty vehicle, an upper hinge point of a hydro-pneumatic suspension cylinder a1 is hinged and fixed with a bracket spherical hinge on a vehicle frame a5, and a lower hinge point is fixed with a steering knuckle a2 by a bolt; one end of a lower cross arm a3 and a lower end face a22 of the steering knuckle a2 are connected by a spherical hinge and are fixed by a bolt, and the other end of the lower cross arm is fixed with a trapezoidal arm a4.
For the independent suspension device as shown in FIG. 1, the existing technical problem is that a trapezoidal steering arm a4 is placed on an upper end face a21 or the lower end face a22 of the steering knuckle. Assuming that the trapezoidal steering arm is mounted on the upper end face a21 of the steering knuckle, H1 is the distance from the center of the upper end face a21 of the steering knuckle to a lower end face a6 of the vehicle frame. Due to the limit of a local section structure of the vehicle frame a5, if upward skipping travels of wheels on a single side are too large, a trapezoidal track rod a4 may interfere with the section of the vehicle frame or other parts and components attached to the vehicle frame, that is, this arrangement will influence the upward skipping travels of the wheels relative to the vehicle frame.
If the trapezoidal steering arm is mounted on the lower end face a22 of the steering knuckle, and H2 is the distance from the lower end face of the steering knuckle to the lower end face of the vehicle frame, since H2 is too high, the design of a transitional steering arm for transferring force and coordinating the movement of left and right steering wheels is a problem.
FIG. 2 shows a schematic diagram of an existing steering arm used in the independent suspension device in which the trapezoidal steering arm is mounted on the lower end face of the steering knuckle. The steering arm assembly is connected and fastened with the vehicle frame b6 or a bracket b6 welded on the vehicle frame through a rotatable pin shaft b5; the trapezoidal steering arm b1 is mounted on the lower end face of the steering knuckle; a steering link assembly b3 transfers movements and forces output from a steering wheel and a steering gear to a trapezoidal track rod b2 through the fan-shaped movement of the steering arm to drive the fan-shaped movement of the trapezoidal arm b1, so as to overcome a steering resistance moment from the ground and achieve the steering of a steering wheel. In order to improve the working stability of the entire steering mechanism including a steering arm device, for the steering arm b4 and the pin shaft b5 in FIG. 2, the second moment of area thereof needs to be improved to improve the bending resistance and the torsional deformation resistance thereof. In this way, the outside diameters of the steering arm b4 and the pin shaft b5 have to be increased, and then the weights are increased accordingly. If the bending strength and the torsional strength of the steering arm b4 and the pin shaft b5 are insufficient, large bending/torsional deformation, breakage, weld cracking and other problems will occur; and moreover, if a certain section of the pin shaft b5 is subjected to bending deformation or breakage, it is costly to grind the pin shaft residual on the vehicle frame bracket and find out a precise position to weld a new pin shaft, and thus the subsequent maintenance cost is increased.